Elastomers with thermoplastic properties have been produced using ABA block copolymers. These block copolymers are the subject of many patents including U.S. Pat. Nos. 3,485,787; 3,830,767; 4,006,116; 4,039,629; and 4,041,103 all assigned to the Shell Oil Company. These block copolymers exist as a styrene--ethylene--butylene--styrene molecular configuration. The overall strength of the polymer is provided by the polystyrene end blocks which act as aggregates or domains which serve as physical crosslinks. The rubbery portion of the polymer is provided by the ethylene--butylene blocks.
The highest temperature at which these block copolymers can operate is limited due to the absence of physical irreversible crosslinks such as those found in conventional elastomers. Additionally, the low glass transition temperature of the polystyrene end blocks further limits the elastomer service temperature. As a result, these ABA block copolymers exhibit a significant amount of creep when subjected to loads at elevated temperatures. This property makes them unsuitable for applications in which stress or load-bearing is required in elevated temperatures.